1. Field of the Invention
The present invention relates generally to the field of wristband antennas for wrist-worn communication devices, and more particularly to an apparatus for sensing the integrity of the wristband antenna.
2. Description of the Prior Art
Due to the small size of wrist-worn communication devices, such as wrist-worn pagers, the antenna system has had to be integrated either wholly, or in part within the wristband of the wrist-worn communication device. One such antenna system which has been utilized in a wrist-worn communication device is described in U.S. Pat. No. 4,873,527 by Tan, entitled "Antenna System for a Wrist Carried Paging Receiver" which provided both a ferrite loop antenna which was located within the housing of the wrist-worn communication device, and a wristband loop antenna which was located within the wristband of the wrist-worn communication device. When a loop antenna was located within the wristband, the loop antenna construction was generally as shown in FIG. 1. Conductors (18, 20) which were integrated within each of the wristband straps (14, 16) were coupled into the device housing to provide the circuit connections to the receiver. The antenna loop was then completed by utilizing the clasp (22), which was normally used to secure the receiver to the user's wrist, to provide the electrical continuity between the conductors located within each of the wristband straps. The integrity of such a wristband loop antenna was dependant on a number of factors, in particular the adequacy of the electrical contact provided by the clasp, the integrity of the conductors within each wristband strap, and the integrity of the connection being provided into the device housing. Maintaining the integrity of a wristband loop antenna was complicated by such factors as flexing of the wristband straps which could over a period of time result in both open circuited conductors within the wristband straps or open circuited connections at the device housing. Both of the problems were at least partly resolved by proper choice of conductor material and providing strain reliefs at the conductor housing interfaces. While such solutions could guarantee the conductor integrity within the wristband sections, such solutions can not guarantee that the user is completely closing the clasp or that contamination build-up is not occurring on the electrical contacts of the clasp, either of which would result in a reduction of the receiver sensitivity. There is a need to be able to sense the integrity of the wristband loop antenna so as to prevent any long term reductions in receiver sensitivity which would ultimately result in the loss of messages being directed to the wrist-worn communication device.